Starting and rotor positioning apparatus for sync pulse-controlled synchronous motors



Ap 7, 1953 w. J. HARSHBARGER 2,634,388

STARTING AND ROTOR POSITIONING APPARATUS FOR SYNC PULSE-CONTROLLED SYNCHRONOUS MOTORS 5 Sheets-Sheet l Filed Feb. 17, 1950 IN VEN TOR. #im 75? J #RWM/Paw? April 7, 1953 w. .1. HARSHBARGER 2,634,388

- STARTING AND RoToR PosITIoNING APPARATUS Foa SYNC PuLsE-coNTRoLLEn sYNcNRoNous MOTORS A Filed Feb. l?, 1950 3 Sheets-Sheet 2 AUNA. vvvvvv INVENTOR. Muff J. #Aww/:652

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April 7, l953 I w J. HARSHBARGER 2,534,388

STARTING AND OTOR POSITIONING APPARATUS FOR SYNC PULSE-CONTROLLED SYNCHRONOUS MOTORS Filed Feb. 17, 1950 3 Sheets-Sheet 3 l: o sTAToe oF Moro/a /o -aG) HIGH VOLTA 6E W j Aa i Y INVENTOR www A Troia/V556 Patented Apr. 7, 1953 STARTING AND ROTOR POSITIONING AP- PARATUS FOR SYNC PULSE-CONTROLLED SYNCHRONOUS MOTORS Walter J. Harshbarger, New York, N. Y.

Application February 17, 1950, Serial No. 144,626

8 Claims.

My invention pertains to apparatus for starting and synchronizing the rotor of a synchronous motor in a predetermined angular position with each occurrence of a series of regularly recurring or sync pulses, and more particularly to apparatus for starting the rotation `of Vand fixing the rotor of the drive motor for motion picture film which is to be televised in a predetermined angular position with the occurrence of a television synchronizing pulse.

In a continuous motion flying spot lm scanning apparatus, such as is disclosed in my copending application for Method of Televising Motion Picture Film, Serial No. 130,134, filed November 30, 1949, the problem arises of accurately positioning the film frame in correct position in the iilm gate aperture in order to insure that the first transverse or horizontal trace of each light raster upon the face of the flying spot tube will scan the leading edge of the corresponding motion picture nlm frame. In the absence of some synchronizing means, the scanner will have to be framed cach time it is started with la particular reel cf film, since there is no physical marking or indication which will show the correct psition in which the film must be placed to insure its proper framing. This is unlike a standard motion picture iilm theatre projector, where the film actually stands still during the projection of each frame and makes its framing procedure relatively simple.

Since each light raster upon the face of the iiying spot tube is initiated by means of television vertical synchronizing or sync pulses, some synchronization of the framing to these sync pulses must be made. In the case of standard 16 mm. lm there is one sprocket hole for each. frame along the length of the lm, and if the film is properly printed this sprocket hole coincides with the center line of the space between adjoining frames. In the televising of 16 mm. film the teeth on the driving sprocket may, therefore, be utilized in determining frame location.

In accordance with my invention I synchronize the position `of the film driving motor rotor with a vertical sync pulse so that one film sprocket hole arrives at a predetermined position axially of the film path simultaneously with that vertical sync pulse.

My invention will be more apparent from the following description when taken with the accompanying drawings in which:

Fig. 1 is a diagrammatic drawing in block and schematic form illustrating a film drive system in accordance with my invention;

' aperture when the first light raster on the face of the flying spot tube begins to be scanned or produced. The film, and hence this particular lm frame, moves across the iilm gate aperture from the above-mentioned edge at the rate of 0.120 inch every l@ of a second. During the continuous lm movement this particular film frame is scanned three times and the next nlm frame in sequence along the film is scanned twice. The next film frame is again scanned three times and the ensuing one twice, etc. Thus the teeth of the film driving sprocket must be so disposed angularly that the leading edge of a film frame is positioned at the edge of the film gate aperture where the flying spot of light is to begin its raster cycle simultaneously with the occurrence Aof the corresponding television vertical sync pulse or impulseswhich initiates the corresponding first flying spot of light raster upon the face of the flying spot tube. Also, the sprocket teeth must be so disposed angularly for successive sync pulses that the film moves 0.120 inch between pulses, and thus travels l0.6 inch (the space occupied by two lm frames) between every six sync pulses.

These conditions may be met by using a twelvetooth sprocket to drive the film and driving this sprocket at R. P. M. to produce the desired 36 feet per minute movement of the film. The `angular displacement of the sprocket teeth is thus 30 degrees and the radius of the sprocket is made suchthat the circumferential difference .between center lines of adjacent teeth is 0.3 inch.

By utilizing a four-pole stator two-pole rotor synchronous motor the angular position of this motor rotor relative to the stator can be fixed and made the same each time a synchronizing impulse occurs. By rotating this rotor at 720 R. P. M. and providing a 6:1 gear reduction between the rotor and the film drive sprocket, one sprocket tooth will occur at a xed angle relative to its fixed sprocket bearing each time the motor rotor assumes its predetermined angular position relative to its stator. Thus the linear position of the lm sprocket holes, and hence the leading edge of each film frame along its path, can be xed coincident with the synchronizing pulse.

This will be more apparent from an examination `of the embodiment of Fig. 1, considering the mechanical portion thereof rst. As above described, a synchronous four-pole stator two-pole rotor drive motor i0 is coupled through 6:1 re- 3 duction gear Il to the lm drive sprocket (not shown).

This drive motor is shown schematically in Fig. 2 and has its four stator poles wound as shown. Its two rotor poles are similarly poled, e. g., so that both are either north poles or south poles, the latter being illustrated. For driving 16 mm. film I have found that a permanent magnet rotor is satisfactory. If additional torque output from the motor is required, as when driving 35 min. film. this permanent magnet rotor could be replaced with an electromagnetic rotor having D. C. coils wound thereon and fed through slip rings.

Assuming that the alternating current passing through the stator coils is at the moment at its maximum value, the stator poles would be poled as shown in Fig. 2 and producing substantially their maximum ux. For this condition, rotor i2 must in its rotation assume either the position shown or a position 180 degrees removed therefrom, with the pole i3 at the right of the drawing and the pole le at the left. Thus, for this condition, the rotor must assume either one of two positions 180 degrees removed from one another. Due to the 6:1 gear reduction provided by gear box l l (Fig. 1) a M30-degree movement of rotor I2 of motor It provides only a Sil-degree movement of the nlm drive sprocket (not shown). sprocket are spaced 30 degrees apart, this insures that no matter which of its two positions rotor l2 assumes, one sprocket tooth of the film drive sprocket will be in a predetermined angular position relative to its iixed bearing as determined by the angular position of rotor l2 shown relative to its stator.

Assuming that rotor l2 of synchronous motor l!) is rotating clockwise, as indicated by the dotted arrow, when the current through the coils of the stator thereafter begins to decrease, the maximum flux of each pole will decrease, the result being a rotating eld which pulls the rotor and causes it to revolve clockwise in accordance with conventional motor theory as the current through the stator coils alternates in polarity.

As shown in Fig. l, a stator phasing motor l of a reversible type and controlled from a suitable supply source is provided. A pinion I5 on the shaft of motor l5 engages a cooperating crown gear il' on the stator of film drive motor l@ which is rotatable relative to its xed base (not shown). Thus by rotation of the stator of film drive motor il] the position of its rotor l2, and hence the position of the film drive sprocket teeth and in turn the position of each film frame along the film path, can be adjusted to insure proper framing at theinstant with the occurrence of each television vertical sync impulse which initiates the flying spot of light raster cycle. A knob It is provided on the other end of the shaft of motor i5 to provide for manual control if desired.

To produce the desired 720 R. P. M. output from rnotor 10 utilizing a four-pole stator requires a supply frequency of 24 cycles per second,

vin accordance with the well-known formula:

120Xfrequency (C. P. S.) No. of stator poles R. P. M.:

y.2i-cycle sine wave generator.

Since the teeth on the lrn drive Referring now to Fig. 3, in line A thereof there are represented the (S0-cycle vertical sync television pulses. Line B shows the result of passing these 60-cycle pulses through a scale-of-5 counter or frequency divider, the result being a pulse coincident with each sixth pulse of line A as shown. Each pulse output or impulse of line B is utilized in the continuous motion flying spot film scanning apparatus of my abovementioned application to initiate the light raster cycle upon the face of the flying spot tube, each raster cycle consisting of ve light rasters in succession, each initiated by a {S0-cycle sync pulse of line A and displaced one from the other upon the face of the dying spot tube so as to scan alternate frames of the film thrice and intervening frames twice.

Thus the 12-cycle pulses of line B of Fig. 3, which correspond to every sixth Vertical sync pulse of line A, can conveniently be utilized to synchronize the position of the film driving motor rotor so as to fix in turn the position of the nlm driving sprocket teeth and thus insure that the leading edge of a lm frame lies at the proper edge of the film gate aperture at that instant. This can be accomplished in accordance with my invention by synchronizing the ZAL-cycle power source for film driving motor` I with the 12-cycle pulse output of line B.

Referring now to both Figs. 1 and 3, the 60- cycle sync pulses of line A (Fig. 3) are fed through frequency divider 28 to produce the 12- cycle pulses of line B (Fig. 3). These 12-cycle pulses are then fed through frequency doubler 2i to produce the :Z4-cycle pulses of line C (Fig. 3), alternate ones of which occur simultaneously with the 12-cycle pulses of line B and every sixth (S0-cycle sync pulse of line A (Fig. 3). These 24cycle pulses of line C are utilized to produce a Zal-cycle synchronized sine wave output from alternating voltage generator 22, which comprises 24-cycle multivibrator 23 and Zl-cycle sine wave Shaper 2d. The 2er-cycle square wave output of multivibrator 23 is shown in dotted lines in line D of Fig. 3 and indicated by the reference character D'. The sine wave output, produced by the passage of wave form D' through sine wave shaper 2li, is shown in full lines in line D of Fig. 3 and is indicated by the reference character D. This Zal-cycle synchronized sine wave output is then amplified by driver 25 before being applied to power amplifier 2, whose output is connected to the stator windings oi film drive motor l0.

Since film drive motor l0 is of the synchronous type, it must be brought up to its synchronous speed by external means. Furthermore, the rotor I2 of motor I0 must, in addition to rotating at its synchronous speed of 720 R. P. M., also have its angular position at the instant of lapplication of power to its stator from power amplier 26 such that the stator and rotor pole relationships are as shown in Fig. 2 or the equivalent thereof. Drive motor l0 is brought up to speed by means of starting motor 39, which is supplied from any 11G-volt 60-cycle source. Preferably, starting motor 30 is of the capacitorstart four-pole synchronous type having a synchronous speed of 1800 R. P. M. Motor 3D is connected to the shaft of drive motor I0 through a 5:2 reduction gear box 3l and a magneticallycontrolled clutch 32. Clutch 32 preferably has only a single tooth so that after motor l0 has its power applied and before clutch 32 is disengaged and starting motor 30 stopped, the position of its rotor-relative to the shaft output of gear box 3| can vary by more than 180 degrees.

The 24-cycle sine wave output of power amplifier 26 can be applied to the stator of motor lil only when power ampliiier switch 35 (Fig. l) is actuated. The actuation of this switch 35 is controlled by comparing the frequency and phase of the output of motor I0, which operates as a generator during starting when driven by starting motor and thus produces a temporary output alternating current, with the occurrence of the l2-cycle synchronizing pulses from frequency divider 20. The voltage and frequency of the stator output of motor i3 when operated as a generator will, of course, vary from zero to the maximum designed voltage for the stator windings and 24-cycles, respectively, as drive motor l0 cornes up to speed. When rotor I2 of drive motor I0 has been brought up tc '120 R. P. M. so that the stator winding output of motor I0 occurs at 24 cycles per second and has reached this designed value, at some instant the phase of this voltage output from the startor will be as shown in line E of Fig. 3 or, in other words, in phase with the corresponding 2li-cycle output of power .a

amplifier 26 (line D of Fig. 3). This is the instant at which power amplifier switch should be actuated.

This phase correspondence between the wave forms of lines D and E of Fig. 3 is determined :.1-

as follows. rFhe stator output of motor ill acting as a generator is passed through a phaseshift circuit 35, which advances the phase of its output 90 degrees relative to that of its input.

The output of phase-shift circuit 35 is shown in line F (Fig. 3) and leads that of line E by 90 degrees. This output of circuit 35 is combined with the l2-cycle pulse of line B (Fig. 3) in mixer to produce an output whose wave form is shown in line G of Fig. 3. This combined outc;

put is fed to power amplifier switch 35, which is suitably biased as by means of potentiometer 31 so that it will be actuated only when the phase of the output of phase-shift circuit 35 is such that the maximum or peak of its sine wave output occurs substantially simultaneously and is in synchronism with a 12-cycle pulse of line B (Fig.

f 3) from frequency divider 20. When this coincidence occurs, power amplier switch 35 is actuated and allows power aniplier 25 to deliver f its 24-cycle output, shown in full lines in line D of Fig. 3, to the stator of drive motor i3.

In Figs. 4a and Ail) are shown in detail the circuitry of the electronic portions of Fig. l with the exception of frequency divider 20 and frequency doubler 2i. Frequency doubler 2i has been omitted in the particular circuitry shown in Figs. 4a and 4b for reasons which will be pointed out hereinafter. Frequency divider 20 may be of any suitable conventional design, such as a scale-ofring counter so as to pass every sixth (iO-cycle vertical sync television pulse. The output of frequency divider 29 is connected through coupling condenser 43 to the cathode of clamper 4i and the plate of isolating diode 42. Clamper tube 4l has its plate connected to ground and is included to insure that only positive synchronizing pulses from frequency divider 2B are passed through isolating diode 42. The

output of isolating diode 42, taken from its cathode, is then passed through blocking oscillator 43 to sharpen the 12-cycle pulses. These sharpened lZ-cycle pulses, taken from the plate of blocking oscillator 43, are coupled to the grid of cathode follower 44 and one grid of mixer 45. The output of cathode follower 44 is connected to the grid of tube 46 of 2li-cycle free-running multivibrator 23. This multivibrator comprises two tubes 4S and 41. Potentiometer 41 is common to the grid circuits of both tubes 45 and 41 and controls the frequency of the multivibrator output. Resistor 48 in the grid circuit of tube 46 and resistor 49 in the grid circuit of tube 41 control the duration of the outputs of the two tubes relative to one another and are utilized to equalize the respective halves of the 2li-cycle square wave output of multivibrator 23.

It will be noted that the frequency doubler 2l of Fig. l has been omitted from the circuitry of Figs. fia and 4b. This is because I have found in this particular circuit that it is necessary only to synchronize every other cycle of the 2li-cycle multivibrator with a l2-cyc1e pulse of line B (Fig. 3) corresponding to one of the 60-cycle sync pulses of line A (Fig. 3).

This 24-cycle square wave output of multivibrator 23, taken from the cathode of tube 41, is directly connected to the cathode of tube 50. Tube and network 5i in the cutput'circuit thereof constitute the 2li-cycle sine wave shaping circuit 24. The resultant 2li-cycle sine wave output is amplied and inverted in tube 52 before application to driver 25. rlhe output of driver 25 is transformer-coupled to the grids of pushpull tubes 53 and 54 of power amplifier 26. The output of push-pull tubes 53 and 54 is then transformer-coupled to the stator windings of lm drive motor l0.

The center tap of the secondary winding of filament transformer 55 feeding the filaments of power amplifier tubes 53 and 54 is returned to ground through contact 56 and armature 51 of relay 58 and switch tube 59 all in series, these elements constituting power amplifier switch 35 of Fig. l. Thus power amplifier tubes 53 and 54 can pass current only when relay 58 is actuated and switch tube 59, which is of the gas type as shown, is conducting.

The bias upon the control grid of switch tube 59 is derived from a D. C. bias rectifier comprising two diodes 60 and 6I connected as shown. This bias is adjustable by means of Slider 52 0f potentiometer 31. The input to switch tube 59, applied to its screen grid, is also adjustable as shown by means lof potentiometer 53 and is derived from the plate of mixer tube 45. One input of mixer tube 45 is derived from blocking oscillater 43 as above described. The other input of mixer 45l consists of the stator voltage output of driving motor i, operating as'a generator,

phase-shifted hy 9G degrees and amplified. This phase shift is obtained by passing the stator voltage output of motor i9 through integrator 64, since integration of a sine wave results in a minus co-sine wave., The output of integrator 54, which corresponds to phase shift circuit 36 of Fig. l, leads its input by 90 degrees, as shown in lines E and F of Fig. 3. This phase-shifted voltage is then amplified and inverted in tube before being applied to mixer 45. As shown, the relative magnitudes of the two inputs to mixer 45 are adjustable by means of potentiometers B6 and 51, respectively.

The operation of the circuit of Figs. 4a and 4b, with the exception of the operation of relay 58, will not be repeated here since it has been described above in connection with Figs. l, 2, and 3. Relay 58, in addition to contact 56 and armature 51, also includes contact 58 and armature 69 connected to apply plate voltage to switch tube 59 egescss at the same time that its plate is' connected to the center tap of lament transformer 55. In the operation of the embodiment of Fig. 1, relay 58 is actuated simultaneously with the application of power to starting motor 3B and magneticallycontrolled clutch 32 as by means of a push-button switch (not shown). So long as this push-button switch is maintained closed, starting motor 3G drives motor l through magnetically-controlled clutch 32. When the output of drive motor It, thus operating as a generator, reaches its proper frequency voltage and phase, as shown in line E of Fig. 3, switch tube 59 will fire as described. This closes the ground return circuit of the center tap of filament transformer 55 and allows power amplifier tubes 53 and 54 to pass current to supply their 24-cyole sine wave output to the stator windingsof film drive motor I0. As soon as the operator sees, from a suitable monitor not shown, that the film is being properly scanned and thus is properly framed, removal of his finger from the push-button switch will cause magneticallycontrolled clutch 3-2 to open and starting motor 3B to stop. However, a hold circuit (not shown) for relay 58 is provided to maintain relay 58 energized so that film drive motor It continues its rotation. A suitable stop switch is, of course, provided in this hold circuit so that the motion of the film and the rotation of lm drive motor I can be terminated when desired, as at the end of a desired film sequence or reel.

While the wave forms of lines A, B, and C of Fig. 3 have all been shown as positive, and the wave forms of lines D, E, F, and G have been shown as positive duringtheir rst half-cycle, it will be apparent to those skilled in the art that these wave forms as utilized at various points in the circuitry of Figs. 1. 4a, and 4b may be inverted as necessary, while still maintaining their shown phase relationship.

Numerous additional applications of the abovedisclosed principles will occur to those skilled in the art and no attempt has here been made to exhaust such possibilities. For example, 24-cycle sine wave generator 22 may comprise an alternating voltage generator which directly develops a sine wave output rather than comprising the v2li-cycle multivibrator 23 whose output is shaped into sine-wave form by 24.-'cycle sine-wave Shaper 24 as shown. Also, a four-pole rotor may be utilized in four-pole stator film drive motor I0 providing the diametrioally-disposed poles are similarly poled. Thus in Fig. 2 rotor l2 would be modified to include a iirst north pole extending upward toward the upper south stator field pole and a second north pole extending downward toward the lower south stator field pole.

The scope of my invention is defined in the following claims, wherein by magneticallypoled rotor is meant a rotor having magnetic poles produced -either by permanent magnetism or by the electrical energization of suitable rotor or armature coils.

I claim:

1. Starting and rotor positioning apparatus for a sync pulse-controlled synchronous motor comprising a sine wave generator adapted to be triggered by the input sync pulses and to produce alternating current of magnitude and frequency suited to drive said motor in synchronism with the pulses, astarting motor adapted to drive the rotor of the synchronous motor at the approximate desired speed and thereby to cause said synchronous motor while under control of the starting motor to generate a temporary output alternating current, a phase-shifting'eircuit arranged to shift the phase of said temporary output current so that some at least of the peaks of said current are in synchronism with said input sync pulses, a mixer for said phase-shifted current and said pulses, and a switch tube receiving the mixer output and biased to produce, in response to the coincidence of a pulse and a peak in the mixer, a connection between the output of said sine Wave generator and the synchronous motor.

2. Starting and rotor positioning apparatus for a sync pulse-controlled synchronous motor comprising a synchronous motor including a four-pole stator, windings therefor, and a magnetically-poled rotor having two similarly-poled diametrically-disposed poles, aV startingv motor connected to said rotor for driving said synchronous motor at substantially its synchronous speed, an alternating voltage generator under control of the sync pulses for generating an alternating voltage in synchronism with said pulses at a frequency in cycles per second equal to one-thirtieth said synchronous speed in revolutions per minute, a phase-shift circuit connected to said stator windings, a switch tube connected to said phase-shift lcircuit and the source of said pulses and biased to operate in response to an input produced by substantial coincidence of one of said pulses and the maximum amplitude output of said phase-shift circuit, and a connection between said stator windings and the output of said generator under oontrol of said switch tube.

3. Starting and rotor positioning apparatus for a sync pulse-controlled synchronous motor comprising a synchronous motor including a four-pole stator, windings therefor, and a magnetically-poled rotor having two similarly-poled diametrically-disposed poles, a starting motor connected to said rotor for driving said synchronous motor at substantally its synchronous speed, an alternoting voltage generator under control of the sync pulses for generating an alternating voltage in synchronism with said pulses at a frequency in cycles per second equal to onethirtieth said synchronous speed in revolutions per minute, a phase-shift circuitconnected to said stator windings, a mixture connected tosaid phase-shift circuit and Aa source of said pulses, a switch tube connected to said mixer and biased to operate in response to an input produced by substantial coincidence of one of said pulses and the maximum amplitude output of said phaseshift circuit,A and a connection between said stator windings and the output of said generator under control of said switch tube..

4. Starting and rotor positioning apparatus for a synchronous motor controlled from (S0-cycle per second sync pulses comprising a synchronous motor including a four-pole staton-windings therefor, and a magnetically-poled rotor having two similarly-poled diametrically-disposed poles, a starting motor connected to said rotor for driving said synchronous motor at substantially its synchronous speed, a scale-offrequency divider connected to the source of the 60-cycle sync pulses, a frequency doubler connected to said frequency divider, a 24-cycle per second sine wave generator connected to said frequency doubier to produce a sine wave output, each of whose cycles is initiated substantially simultaneously with a Zei-cycle pulse from said frequency doubler, a, phase-shift circuit for producing a leading phase shift connected to said stator windings, a mixer connected to said phase-shift circuit and said frequency divider, a s 1itch tube connected to said mixer and biased to operate response to an input produced by substantial coincidence of one of the lZ-cycle output pulses' of said frequency divider and the 'irnuin apli tude output of said phase-shift circuit, and a connection between said stator windings the output of said generator under control of said switch tube.

5. Starting and rotor positioning apparatus for a synchronous motor controlled from SG- cycle per second sync pulses comprising synchronous motor including a fourpole stator, windings therefor, and a magneticallypoled rotor having two similarly-,soleil diametricallyd disposed poles, a starting motor connected to said rotor for driving said synchronous motor at substantially its synchronous speed, a scaleof-5 frequency divider connected to the source of the Gil-cycle sync pulses, a 2li-cycle per second sine wave generator connected to said frequency divider to produce a sine wave output, every other cycle of whch is initiated substantiallsr simultaneously with a l2-cycle pulse from said frequency divider, a phase-shift circuit for pron ducing a 953 leading phase shift connected to said stator windings, a miner connected to phase-shift circuit and said frequency d a switch tube connected to said mixer an to operate in response to an input produce substantial coincidence of one of the output pulses of said frequency divider and i 'e maximum amplitude output ci said phase-shift circuit, and a connection between said stator windings and the output of said generator un:u der control of said switch tube.

6. Starting and rotor positioning apparatus for a synchronous motor controlled from cycle per second sync pulses comprising a chronous motor including a four-pole station, windings therefor, and a magnetically-poied rotor having two similarly-poled diarnetricallydisposed poles, a starting motor connected to said rotor for driving said synchronous motor at second multivibrator connected to saio frequency doubler to produce a squareewave output, each of whose cycles is initiated substantially siniul taneously with a 2li-cycle pulse from fre1 quency doubler, a 2flcycle sine wave shaper con nected to said multivibrator to produce a 2licycle sine wave output in synchronisin with said square-wave output of said multivibrator, a phase-shift circuit for producing a 95 leading phase shift connected to said stator windings, a mixer connected to said phase-shift circuituand the output of said frequency divider, a switch tube connected to said mixer and biased to operate in response to an input produced by substantial coincidence of one of the lZ-cycle output pulses of said frequency divider and the maximum amplitude output of said phase-shift circuit, and a connection between said stator windings and the output of said sine wave Shaper under control of said switch tube.

7. Starting and rotor positioning apparatus for a synchronous motor controlled from Sli-cycle per second sync pulses comprising a synchronous motor including a four-pole stator, windings therefor, and a magnetically-poled rotor having two similarly-poled dianfletrically-disposed poles, a starting motor connected to said rotor for driving said synchronous motor at substantially its synchronous speed, a scale-of-5 frequency divider connected to the source of the SO-cycle sync pulses, a 2li-cycle per second multivibrator connected to said frequency divider to produce a square-wave output, every other cycle of which is initiated substantially simultaneously with a l2-cycle pulse from said frequency divider, a 24- cycle sine wave Shaper connected to said multivibrator to produce a 2lncycle sine wave output in synchronism with said square-wave output of said multivibrator, a phase-shift circuit for pro-i ducing a 90 leading phase shift connected to said stator windings, a mixer connected to said phase=-shift circuit and the output of said frequenoy divider, a switch tube connected to said mixer and biased to operate in response to an input produced by substantial coincidence of one of the i2cycle output pulses of said frequency divider and the maximum amplitude output of said phase-shift circuit, and a connection between said stator windings and the output of said sine wave Shaper under control of said switch tube.

S. Starting and rotor positioning apparatus for a synchronous motor controlled from dll-cycle per second sync pulses comprising a synchronous motor including a four-pole stator, windings therefor, and a magnetioally-poled rotor having two similarly-polled diametrically-disposed poles, a starting motor connected to said rotor for driving said synchronous motor at substantially its synchronous speed, a scale-offrequency divider connected to the source of the Sil-cycle sync pulses, a 2li-cycle per second multivibrator connected to said frequency divider to produce a square-wave output, every other cycle of which is initiated substantially simultaneously with a l2-cyole pulse from said frequency divider, a 24- cycle sine wave shaper connected to said multivibrator to produce a 2li-cycle sine wave output in synchrcnism with said square-wave output of said multivibrator, a phase-shift circuit for producing a 90 leading phase shift connected to said stator windings, a mixer connected to said phase-shift circuit and the output of said frequency divider, a switch tube connected to said mixer and biased to operate in response to an produced by substantial coincidence of one of the lZ-cycle output pulses of said frequency divider and the maximum amplitude output of said phase-shift circuit, a connection between said stator windings and the output of said sine wave Shaper Linder control of said switch tube, and means for rotatably securing said stator in a need based including means for rotating said stator in said securing means.

WALTER, J. HARSHBARGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,732,734 Thomas Cot. 22, 1929 1,796,213 McCrea Mar. 10, 1931 1,796,220 Seely Mar. 10, 1931 2,442,123 Espley et al. May 25, 1948 

